Components which are subject to operating loads, such as for example turbine blades and vanes of gas turbines, are subjected to an electrolyte treatment, so that the component can then be refurbished. In the case of gas turbine blades and vanes, the MCrAlX layers on the component, which are subject to operating loads, are removed by being immersed in 20% strength hydrochloric acid at approx. 50°-80° C. After a period of time derived from values gained through experience, the blades or vanes are removed from the acid bath, rinsed with water and then abrasively blasted. The process sequence of electrolyte bath followed by blasting is repeated a number of times until the entire MCrAlX layer has been removed or dissolved. The repetition of the individual process steps is generally necessary, since the electrolyte only dissolves aluminum-containing phases of the MCrAlX layer close to the surface. Deeper-lying regions of the MCrAlX layer therefore cannot be dissolved in one step. A porous layer matrix remains on the surface and is subsequently removed by blasting, for example mechanically.
The time for which the blades or varies remain in the electrolyte does not in this case reflect the time which is actually required for the individual blade or vane to conclude the dissolution process, but rather is set as standard to a specific time. The residence time in the electrolyte is in this case determined on the basis of general empirical values.
However, each individual component is subject to different levels of load, which means that a fixed preset time leads to different or incomplete dissolution of the surface of the component which is subject to load. In many cases, the components remain in the acid bath until the predetermined period of time has elapsed without any further progress being made in the removal of the coating.
EP 1 094 134 A1 and US 2003/0062271 A1 disclose processes for the electrochemical removal of layers.
U.S. Pat. No. 4,539,087 discloses a method in which the current of an electrolytic process is measured, so that on the basis of the current profile it is possible to reach a decision as to when to terminate the process.